Process for refining metals



Sept. 21, 1943.

J. O. BETTERTON ET AL PROCESS Fok REFINING METALS Filedv oct. 5o, 1941 WH/Z'E METAL, RoJJ-.x 57a JM@ 0F .s/a. g1: 2.4, N/v- RMU/VE /4//7/1 INVENTORS ing to the desired end Patented Sept. 21, 1943 J ese 0. Betterton,

santa Ana, cani., mi 'zum Lebedeif, Metuchen, N. J.,

assignors to American Smelting and Benning Company,

New York,

N. Y., a.l corporation of New Jersey Application October 30, 1941, Serial No. 417,186

(ci. 'z5-s) 8 Claims.

This invention relates to the rening of metals and particularly concerns the removal of nickel from metals and metal alloys of predominantly non-ferrous composition.

In various metallurgical operations looking toward the production of rei'lned non-ferrous metals or alloys, small amounts of nickel are often encountered which must be removed. The problem is of frequent occurrence in reclaiming values from secondary metals such as scrap brassesand bronzes but is not at all uncommon in reining primary metal as, for example, in lead reiining wherein nickel often interferes with the processproduct, of the antimony removed from the lead during the softening stage of the refining process.

` During the ordinary course of refining secondary brass and bronze materials such as above mentioned, there is produced an impure white metal containing important amounts of tin and lead, together with antimony, arsenic, and other components, which latter constituents must be removed in order to produce a marketable solder. This impure white metal contains frequently more or less nickel which, in itself constitutes a valuable product, but which is detrimental to the refining operation and to the refined solder produced therefrom. l

The present invention, therefore, is directed to the removal of nickel from metallic alloys, or

from metallic products wherein the metals are present in the form of inter-metallic compounds,

` the like of suiiicient depth so that the silicon, which is employed preferably as lumps of graphitoidal silicon, sinks through the protective cover slag into engagement with the metal bath therebeneath thereby becoming incorporated therein.

The precautions to be observed incidentto the addition of silicon tothe bath are necessary because f the ease with which the silicon becomes oxidized at the temperature of operation, and the slag not only prevents contact of the silicon with air during the reaction, but also tends to clean off any oxide lms on the surface of the silicon, as the latter sinks through the slag layer. i

Where graphitoidal silicon is being used, which is preferable because of its-being readily available and in a form which easily is reactive, the cover slag should'have a specific gravity of-less than 2.4. Many different slags may be employed for this purpose, among which are sodium silicate, sp. g. 2.3, sodium chloride, sp. g. 2.16; and borax, sp.1g; 2.36; or, the metal bath may be covered simply with a layer of powdered coke or and thickness to exclude the air from the metal bath.

It is usually desirable, where the slag isl normally non-carboniferous, to include a certain amount of reducing agent such as coke or other form of'carbon. In such instances the silicon is simply placed on the sur ace of the slag and sinks through into contact with the metal bath. The

"nbath may be agitated in any suitable manner for there being present in the material being ytreated vonly the metalsthemselves without any substantial inclusions of oxides, sulphides, or other compounds of metals with non-metallic elements.

In accordance with the present invention, the nickel is removed by treating a molten bath of themetaliic material with silicon, tions such that the nickel will combine with the silicon to form a layer floating on the metal bath, which layer contains the nickel as nickel silicide. In practice, the operation is carried out in a reverberatory furnace' at temperatures of from approximately 1800 F. to 2200 the reaction temperature being dependent, of course, upon the composition of the material being treated.

The silicon may be added to the metal bath in any suitable manner, as `by submersion in the bath by the use of a suitable tool for that purposei butpreferably the silicon is added by using a protective slag which is inactive both with respeci tc the metal bath and to the silicon and which has aspeciflc gravity somewhat lower than the specific gravity ofthe silicon being added,

under' condi-" 'ployed to carry lfacilitatingthe incorporation of the silicon therein.

It will be understood that the process embraces l the addition of the silicon to the bath either as the element or in a form in which the silicon may be ,liberated from combination in situ in the bath. Thus, the silicon may be added in alloy form or an electric furnace maybe emout the process and the silicon reduced from silica by the action of carbon at the temperature of the electric furnace'. The preferred practice,y however, is to operate in a reverberatory furnace using a cover slag of sodium silicate, which is utilized in a relatively thin layer. Except where coke is used, the covering layerwill be uid at the temperature of the silicon will sink readily through it, and where coke is used, it is ground to such neness that the resulting powder particles will not offer excessive resistance to the passage of 'the silicon therethrough.

In connection with the cover slag,rand coke `or the like where such is tobe used as a cover instead of a uid slag, it is to be borne in mind that the free-sinking of the silicon therethrough is an important consideration in the operation of the process in order to minimize oxidation of the silicon, it being noted in this connection that where a reverberatory furnace is being used, it is inconvenient and often, impractical to submerge the silicon in the metal bath by mechanical means.

'I'he process of the present invention will be illustrated by theaccompanying drawing, which shows a diagrammatic iiow sheet of the process.

In accordance with the drawing, it will be seen that the nickel-containing material such as "white metal, drosses, alloys, or the like, are smelted and reduced to metal if necessary in order to form a molten metal bath. Obviously, however, if the material being treated already is in metallic condition, as is the case where the material is white metal or is an alloy, the smelting and reduction steps are not necessary, it being then required merely to melt the metal and bring it up to reactive temperature while protecting the metal from oxidation.

The slag resulting from the smelting or melting is discarded, and the resulting molten bath is covered with a relatively thin layer of a suitable slag which, as has been pointed out above, is non-reactive with respect to silicon and the metal bath and which is uid at the temperature of operation. In practice, as has been indicated above, sodium silicate is a preferred slag material for this purpose, although other slags such as borax or common salt may be used, it being important, however, as has been pointed out above, that the slag has a specic gravity less than the specific gravity of elemental silicon, that is to say, a sp. g. of less than 2.4. As has been pointed out above, powdered coke or powdered carbon may be utilized as the protective layer, so long as the particles thereof do not preclude the sinking of the'silicon therethrough into the metal bath.

After the silicon has fully reacted, there is produced a three-layer product, the top layer being essentially slag, the intermediate layer being a silicide layer which contains at least substantially all of the original nickel present, and the bottom layer being the nickel-depleted metal. In removing the charge from the furnace, the molten metal ard the silicide layer containing the silicide formed by the reaction are appropriately drawn i. into a settling vessel with a bottom spout, in which vessel the silicide is allowed to freeze thereby forming a solid crust from beneath which the molten metal is tapped.

The nickel silicide crust, which ordinarily contains from about to about 50% nickel and minor amounts of other metal valuesfis processed for nickel recovery and the clean metal, now substantially free from nickel, is further refined if necessary.

'Ihe process of thepresent invention may be illustrated by the following specic examples:

Example 1 A charge made up of 340 parts by weight of high nickel-copper dross, 340 parts by weight of nickel'crust, and 680 parts by weight of solder dross produced in the rening of secondary brass and bronze, was reduced to metal with coke in the presence of 30 parts by parts by weight of sodium silicate as a cover slag. The reduced metal assayed originally 3.7% Ni.

This resulting mixture was held in molten conweight of silicon and 110,

. from 1800 F. t0 2000 dition in a suitable furnace at a temperature of F. for a suitable length of time to insure complete reaction resulting in three layers: a lower layer of 1090 parts by weight of metal; an intermediate layer of 175 parts by weight and containing the produced silicide; and a top layer of parts by weight of slag.

The metal assayed: Sn 55.2%, Ni 0.3%, Sb 5.5%, As 1.37%. The silicide layer assayed: Sn 1.6%, Pb 1.4%, As 0.9%| Sb 0.6%, Ni 22.4%, Si 17.0%. 'I'he slag assayed only 2.1% Sn and 1.1% Pb.

Example 2 Six hundred parts by weight of impure "white metal" assaying: Sn 37.0%, Pb 40.5%, Ni 5.27%, Sb 5.5%, As 2.1%, were melted in a reverberatory furnace under a 48 parts by weight of sodium silicate cover slag. To the resulting bath were added 36 parts by weight of silicon, which was dropped onto the slag and allowed to sink therethrough.

Upon completion of the reaction, the silicide layer was found to be 74.0 parts by weight and assayed: Ni 42.5%, Sn 2.8%, Pb 1.9%, As 0.3%, Sb 0.9%. The recovered metal, 552 parts by weight, Ashowed a nickel content of only 0.13%.

The term white metal as used in the specification and claims refers broadly to lead-tin a1- loys commonly used for machine bearings and as type metals. These alloys ordinarily contain small but eiiective amounts of one or more modifying constituents, such as, antimony, arsenic, nickel, copper, phosphorus or -other elements. For further denition and description of white metals reference may be made to the publication entitled Materials Handbook, fourth edition by George S. Brady.

It will be thus readily appreciated that the present process effects a simple and direct elimination of nickel from nickel-bearing, predominantly non-ferrous metals and alloys and that while particular adaptations have been mentioned, the process is of general application in the removal of nickel from metals and alloys of the class mentioned.

What is claimed is:

1. The process of removing nickel from nickelcontaining, predominantly non-ferrous lead bear ing metals which comprises reacting upon a molten bath of the said metal with silicon in the presence of an inert cover of material having a specic gravity less than the specific gravity of silicon, thereby causing the silicon to pass therethrough into contact with the metal bath, and removing resulting nickel silicide from the metal bath, the said bath being substantially free from oxygen and sulphur compounds reactive with silicon.

2. The process of removing nickel from nickelcontaining, predominantly non-ferrous lead bear ing metals which comprises forming a molten bath of the metal, protecting the said bath againstv oxidation; introducing silicon into the bath, maintaining the bath at reactive temperature with the silicon to form nickel silicide, and removing the nickel silicide from the bath, the said bath being substantially free from oxides and sulphides reactive with the silicon.

3. The process of removing nickel from nickelcontaining, predominantly non-ferrous lead bearingmetals which comprises forming a molten bath of the said metal in the presence of a protective cover, adding silicon to the bath through the cover and reacting the metal therewith, thereby producing a three-layer product, in which the top layer is essentially slag, the intermediate layer is a silicide layer containing substantially all of the nickel of the original nickel silicide, and the bottom layer is metal at least substantially depleted of its original nickel content.

4. The process according to claim 3 wherein the protective cover for the molten bath comprises borax.

5. -The process according to claim 3 wherein the protective cover for the molten bath comprises a layer of powdered coke of sufllcient neness to allow the silicon to fall freely therethrough.

6. The process of removing nickel from nickelcontaining, predominantly non-ferrous lead bearing metals which comprises forming a molten bath of the metal, covering the resulting moltenv bath of the metal with a cover slag having a specific gravity of less than 2.4, and which is inert with respect both to the bath and the free silicon, and introducing silicon into the bath through the said slag layer while maintaining reacting conditions in the bath thereby producing a three-layer system', in which the top layer is substantially slag, the intermediate layer is a silicide layer containing nickel silicide, and the bottom layer is metal at least substantially depleted of its original nickel content.

7. The process of removing nickel from nickelcontaining white metal which comprises producing a molten bath of the said metal, overlying the said bath with a layer of sodium silicate, introducing silicon into the bath, and maintaining the bath reactive with respect to the silicon thereby producing a three-layer system in which the top layer is essentially slag, the intermediate layer is a silicide layer in which the original nickel content of the metal is concentrated, and the bottom layer is the nickel-depleted metal.

8. The process of rening nickel-containing, predominantly non-ferrous lead bearing metal which comprises producing a molten bath of the metal, incorporating silicon in the bath, maintaining the Abath reactive with respectl to the sili- Icon thereby producing nickel silicide in the bath,

allowing the metal and silicide to separate into layers wherein the nickel silicide floats on the bath, freezing the silicide, and removing molten nickel-depleted metal from beneath the frozen nickel silicide.

JESSE O. BETTERTON. YURII E. LEBEDEFF. 

